The Nation's highways are deteriorating at an accelerated pace and sufficient funds are not available to cope with current needs or meet future requirements. Excess truck weight is one cause that can be controlled. By strictly enforcing their weight laws, states could virtually eliminate the damage being caused by overweight trucks. While controlling truck weights will not eliminate highway deterioration, applying federal weight limits to all trucks on federal-aid highways could substantially reduce this deterioration. National statistics show that at least 22 percent of all loaded tractor-trailers exceed state weight limits. This percentage is even higher for other types of large trucks. Although the Department of Transportation (DOT) supported the 1975 increased federal weight limits, it has no program sufficient to offset related increased costs to preserve the quality of the highways. While the 1975 weight increases were made to save fuel for heavy trucks, all vehicles use more fuel on deteriorated roads, heavier trucks use more fuel, and additional highway repairs require more fuel. DOT has not determined whether there has been an overall fuel saving since the higher limits were allowed. A good weight enforcement program requires effective enforcement techniques, stringent penalties, and adequate staff and funds. States need standards to evaluate their program to enforce weight limits that will enable them to identify problems and reliable alternative solutions.

To help assess proposals for further changes in federal truck weight limits, Congress requested this study through Section 158 of the Surface Transportation and Uniform Relocation Assistance Act of 1987. To conduct the study, the National Research Council convened a special Transportation Research Board committee with experts in pavements, bridges, highway safety, freight transportation economics, motor vehicle design, highway administration, motor carrier operations, and enforcement of motor vehicle regulations. The study focused on four issues identified in the study request that involve potential changes to federal weight limits for Interstate highways: (1) Elimination of existing grandfather provisions; (2) Alternative methods for determining gross vehicle weight and axle loadings; (3) Adequacy of the current federal bridge formula; and (4) Treatment of specialized hauling vehicles--garbage trucks, dump trucks, and other trucks with short wheel bases that have difficulty complying with the current federal bridge formula. For each of these issues, the study committee estimated the nationwide effects of changes in federal limits proposed by the trucking industry, highway agencies, and other groups. Projections of heavy-truck miles by type of truck, region of the country, highway functional class, and operating weight were developed for a base case and alternative truck weight regulatory scenarios. These projections were then used to estimate impacts on truck costs, pavements, bridges, and safety.